1. Field of Invention
The present invention relates to semiconductor devices, and more particularly to a trench Schottky rectifier with semiconductor mesa edge shielding, and its method of manufacture.
2. Description of Related Arts
Schottky rectifiers are widely used in power supply systems, and their primary advantage is the very low forward voltage drop. However, for some applications, Schottky rectifiers are limited by their relatively high reverse biased leakage current, or the low reverse blocking voltage, compared to conventional PN junction rectifiers. The forward voltage drop and reverse biased leakage current are primarily determined by the metal energy barrier height of material deposited on the silicon. A tradeoff between forward voltage drop and reverse biased leakage current has to be made by choosing different barrier metals.
One attempt to minimize the reverse biased leakage current and forward voltage drop simultaneously is disclosed in U.S. Pat. No. 5,365,102 by Manoj Mehrotra and Bantval J. Baliga, and entitled to be “Schottky Barrier Rectifier with MOS Trench”. The disclosure is hereby incorporated by reference. A cross-sectional representation of one embodiment of the referenced disclosure is illustrated in FIG. 1. In this figure, the rectifier 10 includes a semiconductor substrate 12 of the first conductivity type, typically N-type conductivity, having a first face 12a and a second opposing face 12b. The substrate 12 preferably comprises a relatively highly doped cathode region 12c (shown as N+) adjacent to the first face 12a. A drift region 12d of first conductivity type (shown as N) preferably extends from the cathode region 12c to the second face 12b. Accordingly, the doping concentration of the cathode region is preferably greater than the drift region. A mesa 14 having a cross-sectional width “Wm”, defined by opposing sides 14a and 14b, is preferably formed in the drift region 12d. The mesa can be of stripe, rectangular, cylindrical or other similar geometry. Insulating regions 16a and 16b (shown as SiO2) are also provided on the mesa sides. The rectifier also includes an anode electrode 18 on the insulating regions 16a, 16b. The anode electrode 18 forms a Schottky rectifying contact with the mesa 14. A cathode electrode 20 is provided adjacent to the cathode region 12c at the first face 12a. The cathode electrode 20 ohmically contacts the cathode region 12c. 
By introducing a plurality of trenches into the silicon and the anode metal within each of the trenches that is separated by a layer of dielectric material, the electrical field intensity at the metal/silicon Schottky barrier is reduced under the reverse potential, which leads to the lower reverse biased leakage current compared with the conventional planar Schottky rectifiers using the same kind of silicon and metal material.
However, the rectifier shown in FIG. 1 has some disadvantages as follows.
(1) The edge of the mesa directly contacting the metal has a sharp point. The corona discharge effect at this point can lead to the high reverse biased leakage current.
(2) The dielectric layer near the mesa edge on the trench sidewalls could be damaged during the dielectric-layer-on-mesa-top (hard mask) removing processes. The direct contact of the anode metal and the mesa sidewall can lead to the high reverse biased leakage current.
(3) The step coverage of the metal is limited. The voids within the trenches posting a high depth-to-width ratio trench metal filling could degrade the performance and reliability of the trench Schottky rectifier.